The 3rd Generation Partnership Project, 3GPP, is responsible for the standardization of the Universal Mobile Telecommunication System, UMTS, and Long Term Evolution, LTE. The 3GPP work on LTE is also referred to as Evolved Universal Terrestrial Radio Access Network, E-UTRAN. LTE is a technology for realizing high-speed packet-based communication that can reach high data rates both in the downlink and in the uplink, and is thought of as a next generation mobile communication system relative to UMTS. In order to support high data rates, LTE allows for a system bandwidth of 20 MHz, or up to 100 Hz when carrier aggregation is employed. LTE is also able to operate in different frequency bands and can operate in at least Frequency Division Duplex, FDD and Time Division Duplex, TDD, modes.
Device-to-device communication is a well-known and widely used component of many existing wireless technologies, including ad hoc and cellular networks. Recently, device-to-device, D2D, communications as an underlay to cellular networks have been proposed as a means to take advantage of the proximity of communicating devices and at the same time to allow devices to operate in a controlled interference environment. D2D is also interchangeably called proximity services, ProSe. ProSe is also the terminology used in the 3GPP LTE specifications. Similarly D2D operation is also interchangeably called ProSe operation and a D2D capable wireless device is also interchangeably called a D2D User Equipment, UE, or a ProSe UE.
In other words, D2D communications enable devices in the proximity of each other to communicate in a peer-to-peer (i.e. direct) fashion rather than communicating through some wireless access point or base station. In practice, ProSe UEs in the 3GPP LTE system utilize the cellular uplink spectrum, i.e. they transmit ProSe signals or channels in the uplink part of the spectrum.
According to state of the art solutions, D2D operation by a UE is performed in a half-duplex mode, i.e. the UE can either transmit D2D signals/channels or receive D2D signals/channels. There may also be D2D relay UEs that may relay some signals to other D2D capable UEs. There is also control information for D2D, some of which is transmitted by UEs and the other is transmitted by eNBs (e.g., D2D resource grants for D2D communication transmitted via cellular DL control channels). The D2D transmissions may occur on resources which are configured by the network or selected autonomously by the D2D enabled UE.
In LTE, when a ProSe UE is in ONC then ProSe operation is allowed only in licensed geographical areas. Hence, the UE has to detect its location, which may be done e.g. by using a Global Navigational Satellite System, GNSS, such as the Global Positioning System, GPS, and find whether it is in a Licensed Area, LA, or in unlicensed areas, ULA.
With the existing solution, the UE must stop ProSe operation when in ULA. This means the UE cannot use ProSe on preconfigured resources. This can be a major limitation under warning or public safety situations etc. since terminating ProSe operation may put life and property at risk.
Furthermore, in certain locations the UE may not be able to detect or cannot reliably determine its location such as in areas without GNSS coverage or with poor GNSS coverage. Therefore it has to stop ProSe operation when ONC if it cannot find its location e.g. due to lack of GPS coverage such as in tunnels. In this situation the UE is required to stop ProSe operation to prevent interference towards WAN/cellular or other network e.g. network managing medical equipment. This can also be a major limitation under warning or public safety situations.